The presently disclosed embodiments relate generally to layers that are useful in imaging apparatus members and components, for use in electrophotographic, including digital, apparatuses. More particularly, the present embodiments pertain to an improved imaging member comprising a single layer in which the single layer further comprises photoactive materials as a hole transport molecule in a polymeric binder. Unlike conventional single-layer photoreceptors, the embodiments are free of photosensitive pigments and traditional electron transporting small molecules. In addition, the imaging member relies on ultra violet (UV) photogeneration of electron hole pairs in the hole transport molecule itself to discharge the surface potential of the imaging member and create a latent image.
In electrophotography, also known as xerography or electrophotographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment moves under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Typical multi-layered photoreceptors or imaging members have at least two layers, and may include a substrate, a conductive layer, an optional undercoat layer (sometimes referred to as a “charge blocking layer” or “hole blocking layer”), an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, and an optional overcoating layer in either a flexible belt form or a rigid drum configuration. In the multi-layer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance. Multi-layered flexible photoreceptor members may include an anti-curl layer on the backside of the substrate, opposite to the side of the electrically active layers, to render the desired photoreceptor flatness.
A drawback to the multi-layered photoreceptors is that such photoreceptors are costly and complicated to manufacture and maintain. Ideally, single layer photoreceptors would be used due to their simple design and cost efficiency. Such photoreceptors are disclosed in U.S. Pat. Nos. 7,070,892 and 7,223,507, and U.S. Publication Nos. 20040197685 and 20050164106, which are hereby incorporated by reference in their entireties. Single layer organic photoreceptors represent the most efficient photoreceptor structure for resolution, cost of manufacture and maintenance and manufacturing simplicity. The main advantages over multi-layer photoreceptors stem from the generating property of the top-surface of the single layer design. Photogeneration at the top surface eliminates the need for anti-plywood treatment of the substrate and also eliminates charge spreading, thus facilitating higher resolution imaging. In addition, single layer photoreceptors allow for greater layer thickness to be used for the single layer and provides for more wear resistance and thus longer photoreceptor life.
However, there are obstacles to obtaining a single layer photoreceptor that operates as desired. The difficulty in designing a usable single layer photoreceptor lies in the selection of compatible hole and electron transport materials, which must also be compatible with the selected charge generating material, typically a pigment, and the binder, and have resulted in failure due to poor discharge performance. Many problems need to be overcome including charge acceptance for hole and/or electron transporting materials from photoelectroactive charge generating material. In addition to electrical compatibility and performance, a material mix for forming a single layer photoreceptor should possess the proper rheology and resistance to agglomeration to enable acceptable coatings. Because it is very difficult to find a combination that meets all of the above requirements, multi-layered devices have generally been used.
Thus, there is a need for an improved photoreceptor design, such as a single layer device, that avoids the problems such as that described above.
The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrophotographic” is generally interchangeable with “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”